ODBC, which, along with every other database API released by Microsoft in the past decade, is not supported in Metro. Astonishingly, it currently appears to be

ODBC, which, along with every other database API released by Microsoft in the past decade, is not supported in Metro. Astonishingly, it currently appears to be easier to query a Microsoft SQL Server from an iOS app than from a Metro-style app. Presumably someone could port ODBC and a driver like FreeTDS to Metro, but it'd be made more difficult by the radically different networking APIs, and would still suffer from annoying limitations like the inability to connect to local database server instances (per Windows Store policy).